JPS60157738A - Optical information detector - Google Patents

Abstract

PURPOSE:To eliminate almost completely the noise induced by the return light as well as the influence of a diffraction effect due to a pit, by setting concave and convex lenses having circular openings centering on the optical axis so that the relfected light passes through both lenses and also using a photoelectric transducer divided concentrically int plural parts to a photodetecting means. CONSTITUTION:Reflected light given from a disk 5 is made incident on a photodetector 8 after passing through a concave lens 6 and a convex lens 7 having circular openings. In this case, the focal position of the lens 6 is coincident with of the lens 7. The light beams received the effects of both lenses and the light beams received no effect of lenses are discontinuous at dark areas shown by oblique lines. A photodetector 8 is divided into 8a-8d, and a focusing error can be detected by obtaining a differential output between detectors 8b and 8c. Both 8b and 8c receive no light in a focusing mode. This can avoid the effects due to an uneven distribution of intensity caused by a diffraction effect of a pit or the control band noise due to the return light.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an optical information detection device which is an essential device for optical discs. The performance required of an optical information detection device is extremely strict, with a focusing error of ±2 μm and a tracking error of ±0, 1 μm. In order to meet this performance, it is necessary to stabilize the semiconductor laser that serves as the light source or to improve the surface area of the disk.

[Prior art]

Furthermore, in the conventional error signal detection method, since the differential output of the divided photoelectric conversion elements that are constantly irradiated is used as the error signal, there are the following drawbacks. In general, in original information detection devices, since the light source is a semiconductor laser, an optical isolator is installed in order to eliminate return induced noise (I MHz to 20 MHz), but due to the birefringence of the disk or the temperature characteristics of the optical isolator, Therefore, it is impossible to completely return to the original state. Therefore, focus or track control range (several Hz to several KHz)
The occurrence of noise can also be seen. Furthermore, recently, as a method of reducing return light induced noise, a method of actively increasing the return light has been adopted, and some devices do not include an optical isolator. However, as a result, noise in the control area often appears even more prominently, which is a serious problem. Also, D r a w (Direc
A similar phenomenon occurs in original discs using the t Read After Write (t Read After Write) method, and as the control signal becomes unstable, the accuracy of the written bit shape or arrangement decreases, which directly affects the s/ A problem has arisen in that it affects 1J. Furthermore, the diffraction effect G caused by the bits of the disk also causes problems such as unstable focusing control.

[Purpose of the invention]

SUMMARY OF THE INVENTION Therefore, the present invention provides an optical information detection device equipped with a focus error detection system that can almost completely eliminate the effects of induced noise caused by returned light or diffraction effects caused by bits.

[Structure of the invention]

Next, the present invention will be explained in detail based on examples. 1st
The figure is a configuration diagram of an optical information detection device of the present invention. A light beam emitted from a semiconductor laser 1 is collimated by a collimator lens 2, passes through a beam fritter 6, enters an objective lens 4, and forms a spot on a disk 5. Again, the reflected light from the disk 5 passes through the objective lens 4 and enters the perforated concave lens B via the beam splitter 6. Here, the light beam passing through the hole maintains the same divergence angle or convergence angle, passes through the hole of the next large convex lens 7, and enters the photodetector 8. At the perforated concave lens B, the light beam subjected to the lens action becomes diverging light and enters the hexagonal convex lens 7, and further receives the lens action and enters the photodetector 8.

Here, the focal position of the apertured concave lens 6 and the focal position of the large aperture convex lens 7 coincide. The important thing is that the light rays that have been subjected to the lens action by the concave and convex lenses, and the light rays that have passed through the hole and have not been subjected to the lens action, are in the dark part (
This is due to the discontinuity caused by diagonal lines). FIG. 2 is a plan view of the photodetector 8. 8α~8d
shows a divided photodetector. next,
The focus detection principle will be explained using FIG. 6. Third
In the figure, the photodetector 8 is shown by a solid line in the cross-sectional view so that the state of division can be seen. First, FIG. 3(a) shows a case where the disk 5 is too close to the objective lens 4 in FIG. Here, the reflected light is a diverging light, and when it enters the holed concave lens 7, the light beam that passes through the hole maintains the same divergence angle and passes through the hole of the holed convex lens 7 and becomes a photo. reaches detector 8. Here, the reached position is divided photodetector f3a
.

and part of 8b. In addition, the light rays subjected to the lens action of the hole-opening concave lens B further increase the divergence angle and enter the large-open convex lens 7, and by the lens action, the divergence angle becomes smaller and reaches only 8d of the photodetector 8. do. Here, the outputs of the divided photodetectors 8α to 8d are A, B, and O, respectively.

When expressed as D, the differential output (B-0) has a positive value since c=0 (10B) since the light does not reach 8c.

Next, Tsubaki 3 (b) shows the state in focus, and disk 5. The reflected light from the lens becomes parallel light and enters the concave hole lens B. The light beam that has passed through the hole passes through the hole in the large convex lens 7 as parallel light and reaches the photodetector 8 at 80.
Reach L. In addition, the light rays subjected to the lens action by the perforated concave lens 6 become diverging light and enter the perforated convex lens.
Reach d. Therefore, the differential output (E-c) is B=
Since O, O=0, it becomes zero.

Next, FIG. 3(C) shows a case where the disk 5 moves too fast from the objective lens 4. In this case, the reflected light from the disk 5 becomes focused light and enters the perforated concave lens 6Q. The light beam that has passed through most of the light beams maintains the same convergence angle, passes through the hole of the large convex lens 7, and reaches 8α of the photodetector 8. Furthermore, the light rays subjected to the lens action by the large aperture lens 6 become diverging light, and become divergent light through the large aperture convex lens 7.
The light enters the photodetector 8, becomes a focused light due to the lens action, and reaches a portion of the photodetector 8d and 8C.

Therefore, since the light does not reach 8b, the differential output (B-C) becomes B=O, and the differential output becomes negative at (-C).

Therefore, by interchanging the differential outputs (B-0) of the divided photodetectors 8b and 80, focusing errors can be detected.

As described above, in the original information detection device of the present invention, since no light hits the divided photodetectors Bb and 8c during focusing, even if the intensity distribution becomes uneven due to the diffraction effect of the pits, or due to the return light. Even if control area noise occurs,
The differential output (B-0) remains at zero, and the focused state can be maintained. In addition, with the conventional method where light hits the photodetector for focusing error detection at all times, including when focusing, if the light deviates slightly from the focused position, the differential output will be reversed due to the diffraction effect caused by the pits. As a result, a reversal of positive and negative values may occur. However, in the optical information detection device of the present invention, one of the differential outputs CB-0) and B or C is always zero when out of focus. is not reversed due to diffraction effects. Therefore, even if there is a slight deviation from the in-focus position, a focus error signal can be detected with high accuracy.

Next, other implementation columns Q will be explained using FIG. The fourth VA is the photodetector 8a of FIG. 2 divided into four parts, and is a photodetector that enables tracking error detection by a heterodyne method. The pupils are set so that the tangential direction (in the arrow) of the disc track coincides with the direction of the dark line dividing the divided photodetectors 8α1 to F3a4.7 Here, the divided photodetectors 8α1 to 8α4 to 8d
The focusing error signal, tracking error signal, and main signal circuit for checking the presence or absence of pits are shown in FIG. (B-C) is given and appears at the output terminal 19. Next, the tracking error signal is the diagonal sum of the photodetectors 8a1 to 8a4, respectively, and is added (A2 + A4) t ( At +
As ) is given, and the subtracter 14 gives a differential output ((
A1+As) (A2+A4)) is given. Then, it appears at the output terminal 17. The final tracking error signal is given by performing heterodyne detection on the output of the output terminal 17. Finally, the main signal is
It is given by adders 9, 10, 12, 13, 15, and 16 as the output sum of all the divided photodetectors, and appears at the output terminal 18.

〔Effect of the invention〕

As described above, in the second embodiment 1, it has been shown that tracking error detection using the hetero gain method is also possible. Further, if the divided photodetector 8d- is divided into two parts, a bush-pull method is also possible, and it is a great advantage that there is a considerable degree of freedom in selecting the detection method. In any case, according to the present invention, highly accurate focusing error detection is possible, so very stable focusing control is possible. Along with this, the accuracy of tracking error detection also becomes extremely high, and tracking control also operates stably.

As described above, the optical information detection device of the present invention has great practical value despite the simple structure of the detection optical system, and greatly contributes to the optical disk system.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the configuration of an optical information detection device according to the present invention. 1... Semiconductor laser 2... Collimator lens 6...
・・・Beam splitter 4・・・・・・・・・Objective lens 5・・・・・・・・・Disc 6・・・・・・・・・Concave hole lens 7・・・・・・・・・- Hole convex lens 8...Photodetector FIG. 2 is a plan view of the photodetector 8. 8a to 8d...Each divided photodetector 3rd
Figures ((L), (b), and (C) are diagrams showing the focus detection principle. 6... Concave lens with hole 7... Hole Convex lens 8... Photodetector Fig. 4 is a plan view of the photodetector 8 used in the second implementation group. 8α1 to 8α4... Each divided photodetector 8b ~8d...Each divided photodetector Arrow Q...Tangential direction of the track Fig. 5 shows a circuit that provides a detection signal in the optical information detection device shown in the second embodiment 1flJ. 8αl to 8α4...Each divided photodetector 8b to 8d...Each divided photodetector 9.
10, 12, 13, 15.16... Adder 11
．． 14...Subtractor 17...Tracking error signal pre-stage output terminal 18...Main signal output terminal 19...Focusing error signal output terminal fitting Upper

Claims (4)

[Claims] (1) A concave lens having a circular aperture centered on the optical axis in an optical information detection device comprising a light source, a means for focusing the light beam emitted from the light source onto an object surface, and a means for receiving reflected light from the object surface. and a convex lens arranged so that the reflected light passes through. (2) The first aspect of the present invention is characterized in that a photoelectric conversion element divided into a plurality of concentric bands is used as a means for receiving the reflected light passing through the concave lens and the convex lens.
Optical information detection device described in Section 2. (3) Optical information detection according to claim 2, characterized in that a circular light-transforming element located at the center of the photoelectric conversion element divided into a plurality of concentric bands is divided into a plurality of parts. Device. (4) The optical information detection device according to claim 1, wherein the concave lens and the convex lens are arranged so that their focal positions match.